Moving up to the senior ranks, Stewart took the European Indoor 3,000m title in a UK record time, claimed the AAA 5,000m title and won 5,000m gold at the 1969 European Athletics Championships in Athens.
Representing Scotland at the 1970 Commonwealth Games in Edinburgh, he ran one of the greatest races of all time to claim victory in the 5,000m final. Roared on by a partisan crowd, he defeated world record-holder Ron Clarke and Olympic 1,500m champion Kip Keino, setting a new European record of 13:22.8.
After battling back from illness and injury, he headed to Munich for the 1972 Olympics. In the final of the 5,000m he suffered a heavy knock from American Steve Prefontaine on the last lap, but produced an amazing burst in the home straight to win the bronze medal.